<?php

class User
{
    private $login;
    private $password;

    public function __construct($_POST['login'], $_POST['password'])
    {
        if(!empty($_POST['login']) && !empty($_POST['password'])){

            $this->login = $_POST['login'];
            $this->password = $_POST['password'];

        } else {

            die;
        }
    }

    public function getData()
    {
        var_dump([$this->login, $this->password]);
    }

}

$newUser = new User($_POST['login'], $_POST['password']);

$newUser->getData();
?>